In this paper, we report enhanced performance of inverted polymer solar cells composed of poly[2,3-bis-(3-octyloxyphenyl)quinoxaline-5,8-diyl-alt-thiophene-2,5-diyl] (TQ1):[6,6]-phenyl-C(71)-butyric acid methyl ester (PC(71)BM) blends by using poly(ethylene oxide) (PEO)-modified ZnO as an electron transport layer. It is found that PEO modification to the ZnO nanoparticle surface can effectively passivate the surface traps of ZnO, suppress the recombination loss of carriers, reduce the series resistance, and improve the electrical coupling of ZnO/active layer. Consequently, both the short-circuit current (J(SC)) and the fill factor (FF) of the inverted solar cells are considerably improved. The resulting power conversion efficiency (PCE) is improved to 5.64% as compared to 4.5% of the reference device using a ZnO electron transport layer. Moreover, this approach can also successfully improve the J(SC) and FF of anther inverted solar cell composed of poly[N-9″-hepta-decanyl-2,7-carbazole-alt-5,5-(4',7'-dithienyl-2',1',3'-benzothiadiazole)] (PCDTBT):PC(71)BM blends. The PCE of the device based on the PEO-modified ZnO layer is increased to 6.59% from 5.39% of the reference device based on the ZnO layer.